Pump system with high pressure restriction

ABSTRACT

A pumping system for a fuel injection system includes a body defining a high pressure pumping chamber, a plunger, a high pressure outlet, a high pressure fluid line connecting the pumping chamber to the outlet, a control valve along the fluid line, and a valve and restriction arrangement along the fluid line. The valve and restriction arrangement includes a restriction and a valve body. The valve body is movable between an open position in which fuel flow from the pumping chamber is generally unrestricted by the restriction and a closed position in which fuel flow from the pumping chamber is significantly restricted by the restriction to store energy in the pumping chamber. Advantageously, the high pressure restriction concept may be utilized in a pumping system for various types of rate shaping, including boot injection and square injection, in addition to pilot operation and post injection operations, and others.

TECHNICAL FIELD

[0001] This invention relates to pump systems for fuel injectionsystems.

BACKGROUND ART

[0002] Engine exhaust emission regulations are becoming increasinglyrestrictive. One way to meet emission standards is to precisely controlthe quantity and timing of the fuel injected into the combustion chamberto match the engine cycle. For certain engine operating conditions,effective injection rate shaping may result in reduced levels ofparticulates and oxides of nitrogen in the engine exhaust. One form ofeffective rate shaping injects fuel slower during the early phase of thecombustion process, resulting in less engine noise.

[0003] Existing rate shaping techniques attempt to control injectionrates by making various modifications to the injector nozzle assembly.Although these existing rate shaping techniques have been employed inmany applications that have been commercially successful, there is aneed for a rate shaping technique that allows more precise rate shapingthan the existing modified injector nozzle assemblies.

DISCLOSURE OF INVENTION

[0004] It is, therefore, an object of the present invention to provide apump system utilizing a high pressure restriction to precisely controlquantity and timing of fuel injected into the combustion chamber of aninternal combustion engine.

[0005] In carrying out the above object, a pump system for a fuelinjection system is provided. The pump system comprises a body defininga high pressure pumping chamber, a plunger disposed in the pumpingchamber for pressurizing fuel, a high pressure outlet, and a highpressure fluid line connecting the pumping chamber to the outlet. Thesystem further comprises a control valve along the fluid line, and avalve and restriction arrangement along the fluid line. The controlvalve includes a first valve body movable between a closed position andan open position. In the closed position, pressurized fuel is routedfrom the pumping chamber to the outlet. In the open position, pressurerelief is provided to the fluid line. The valve and restrictionarrangement includes a restriction and a second valve body. The secondvalve body is movable between an open position and a closed position. Inthe open position, fuel flow from the pumping chamber is generallyunrestricted by the restriction. In the closed position, fuel flow fromthe pumping chamber is significantly restricted by the restriction tostore energy in the pumping chamber.

[0006] The pump system of the present invention advantageously utilizesa high pressure restriction to affect control over the quantity andtiming of the fuel injected into the combustion chamber. In oneembodiment, the body is a unit pump body, and the high pressure outletis configured for flow communication with a fuel injector. In anotherembodiment, the body is a unit injector body and defines a needlechamber. An injector nozzle assembly is in flow communication with thehigh pressure outlet. The injector nozzle assembly includes a needlereceived in the needle chamber. The needle chamber receives pressurizedfuel from the pump outlet. That is, embodiments of the present inventionare suitable for use in both unit pumps and unit injectors.

[0007] In some embodiments, the second valve body is configured as apressure-balance valve. In a particular application, the second valvebody open position provides a flow cross-sectional area, not includingany effective flow cross-sectional area of the restriction, of about twoto three millimeters squared. In some embodiments, the second valve bodyis configured as a pressure-balanced spool valve, and utilizes a throughpassage as the restriction.

[0008] Depending on the particular type of control over fuel injectionquantity and timing that is desired, the valve and restrictionarrangement may be located between the pumping chamber and the controlvalve, or alternatively, the valve and restriction arrangement may belocated between the control valve and the outlet. For example, a valveand restriction arrangement of the present invention between the pumpingchamber and the control valve allows effective control for pilotinjection, boot injection, square injection, and post injection. On theother hand, a valve and restriction arrangement located between thecontrol valve and the outlet allows effective control over pilotoperations and boot injection.

[0009] Further, in carrying out the present invention, a method ofcontrolling a pump system for a fuel injection system is provided. Thepump system has a body defining a high pressure pumping chamber, aplunger disposed in the pumping chamber for pressurizing fuel, a highpressure outlet, and a high pressure fluid line connecting the pumpingchamber to the outlet. A control valve along the fluid line includes afirst valve body movable between a closed position and an open position.In the closed position, pressurized fuel is routed from the pumpingchamber to the outlet. In the open position, pressure relief is providedto the fluid line. The method comprises controlling a valve andrestriction arrangement along the fluid line. The valve and restrictionarrangement includes a restriction and a second valve body. The secondvalve body is movable between an open position and a closed position. Inthe open position, fuel flow from the pumping chamber is generallyunrestricted by the restriction. In the closed position, fuel flow fromthe pumping chamber is significantly restricted by the restriction tostore energy in the pumping chamber. The valve and restrictionarrangement is controlled so as to control fuel flow from the pumpingchamber to the outlet.

[0010] Advantageously, the method may be utilized to affect varioustypes of control over the quantity and timing of the fuel injected intothe combustion chamber. In an embodiment of the invention that reducesthe rate of injection, the method further comprises closing the controlvalve for an injection by moving the first valve body to the closedposition, and restricting fuel flow from the pumping chamber by movingthe second valve body to the closed position to reduce an injectionrate, while the control valve is closed. For a pilot injection, themethod further comprises closing the control valve, restricting fuelflow from the pumping chamber while the control valve is closed, andthereafter, opening the control valve by moving the first valve body tothe open position, ending the reduced rate pilot injection.

[0011] In a boot injection, the method further comprises closing thecontrol valve for injection by moving the first valve body to the closedposition, and restricting fuel flow from the pumping chamber by movingthe second valve body to the closed position to reduce an injection rateand store energy in the pumping chamber, while the control valve isclosed. Further, for a boot injection, the method further comprisesunrestricting fuel flow from the pumping chamber by moving the secondvalve body to the open position to increase the injection rate, whilethe control valve is closed, and thereafter, opening the control valveby moving the first valve body to the open position, ending the bootinjection.

[0012] For square injection, the valve and restriction arrangement islocated between the pumping chamber and the control valve, and themethod further comprises opening the control valve by moving the firstvalve body to the open position, restricting fuel flow from the pumpingchamber by moving the second valve body to the closed position to storeenergy in the pumping chamber, while the control valve is open. Themethod further comprises, thereafter, closing the control valve bymoving the first valve body to the closed position, and unrestrictingfuel flow from the pumping chamber by moving the second valve body tothe open position to increase the injection rate, while the controlvalve is closed.

[0013] For reducing plunger noise, the valve and restriction arrangementis located between the pumping chamber and the control valve and themethod further comprises closing the control valve by moving the firstvalve to the closed position, and unrestricting fuel flow from thepumping chamber by moving the second valve body to the open position,while the control valve is closed. The method further comprises,thereafter, opening the control valve by moving the first valve body tothe open position, and restricting fuel flow from the pumping chamber bymoving the second valve body to the closed position to reduce pressurerelease at the plunger, while the control valve is open.

[0014] For post injection, in addition to reducing the rate of pressurerelease at the plunger, the method further comprises, closing thecontrol valve by moving the first valve body to the closed position.Further, thereafter, fuel flow may be unrestricted from the pumpingchamber by moving the second valve body to the open position to increasean injection rate for post injection, while the control valve is closed.

[0015] The advantages associated with embodiments of the presentinvention are numerous. For example, pumping systems such as unit pumpsor unit injectors made in accordance with the present invention utilizea high pressure restriction to allow more precise control over thequantity and timing of injection into the combustion chamber.Embodiments of the present invention allow sophisticated control overthe quantity and timing of injection and may be utilized to perform, forexample, pilot operation, rate shaping including boot injection orsquare injection, and post injection, in addition to reducing the rateof pressure release at the plunger after an injection, to reduce noise.

[0016] Further, it is appreciated that the valve and restrictionarrangement may be located between the control valve and the plungerchamber or alternatively between the control valve and the outletdepending on the particular control techniques to be performed. Bootinjection may be utilized to reduce oxides of nitrogen, while squareinjection may be utilized during high exhaust gas recirculation rates toreduce particulates. Further, embodiments of the present invention maybe utilized to perform multiple injections into the combustion chamberduring a single cycle.

[0017] The above object and other objects, features, and advantages ofthe present invention will be readily appreciated by one of ordinaryskill in the art from the following detailed description of the bestmode for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a schematic diagram of a first embodiment of the presentinvention;

[0019]FIG. 2 is a schematic diagram of a second embodiment of thepresent invention;

[0020]FIG. 3 is a side elevation, in section, of a unit pump of thepresent invention;

[0021]FIG. 4 is a side elevation, in section, of a unit injector of thepresent invention;

[0022]FIG. 5-8 are enlarged views of the control valve and the valve andrestriction arrangement in an exemplary embodiment of the presentinvention, showing the valve bodies in various operational positions;

[0023]FIG. 9 is a graph depicting valve areas during a boot injection;

[0024]FIG. 10 is a graph depicting pressure versus cam degrees during aboot injection;

[0025]FIG. 11 is a graph depicting fuel delivery versus cam degreesduring a boot injection;

[0026]FIG. 12 is a graph depicting pressure versus cam degrees during aboot injection;

[0027]FIG. 13 is a graph depicting fuel delivery versus cam degreesduring a boot injection;

[0028]FIG. 14 is a graph depicting valve areas during a squareinjection;

[0029]FIG. 15 is a graph depicting pressure versus cam degrees during asquare injection;

[0030]FIG. 16 is a graph depicting fuel delivery versus cam degreesduring a square injection;

[0031]FIG. 17 is a graph depicting valve area versus cam degrees duringa post injection;

[0032]FIG. 18 is a graph depicting pressure versus cam degrees during apost injection;

[0033]FIG. 19 is a graph depicting fuel delivery versus cam degreesduring a post injection; and

[0034]FIG. 20 is a preferred value arrangement for use in pumps andinjectors of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] A pump system for a fuel injection system is generally indicatedat 10, in FIG. 1. An engine driven cam 12 drives a plunger 14. Thepumping chamber of plunger 14 is connected to an injector via a highpressure fluid line. In embodiments of the present invention, the pumpsystem may be a unit pump connected via a high pressure fluid line to aninjector, or alternatively, may be a unit injector. Further, it isappreciated that embodiments of the present invention are broadlyillustrated in FIGS. 1 and 2, and that the exemplary implementations inFIGS. 3 and 4 are included for illustration purposes. That is, there aremany different ways to implement embodiments of the present invention inaccordance with the schematic illustrations in FIGS. 1 and 2. Withcontinuing reference to FIG. 1, a valve and restriction arrangement isgenerally indicated at 15, and includes high pressure restriction 16 andvalve 18. As shown, the valve body is movable between a closed positionthat causes fuel flow through the high pressure fluid line to besignificantly restricted by restriction 16 to store energy in thepumping chamber at plunger 14. In the open position, restriction 16generally does not restrict fluid flow through the high pressure line,as fluid flow may pass through valve 18. It is appreciated thatsignificantly restricted by restriction 16 means that there is anoticeable pressure difference between the pumping chamber and the otherside of the restriction (the unit pump outlet or the unit injectorneedle chamber). That is, significantly restricted means restrictedsufficiently to reduce the rate of injection for a boot injection, orreduced rate pilot injection, etc. Further, generally unrestricted (whenvalve 18 is open) means that flow through restriction 16 is minimal andinjection events may occur normally.

[0036] With continuing reference to FIG. 1, the control valve 20 isclosed to route pressurized fuel from the pumping chamber to the pumpingsystem outlet, which in turn, connects to injector 22. When controlvalve 20 is open, fuel flow from the pumping chamber bypasses the pumpsystem outlet to low pressure reservoir 24. It is appreciated that thecontrol valve is preferably positioned between the valve and restrictionarrangement 15 and the pump system outlet. Alternatively, a controlvalve 26 may be located between the valve and restriction arrangementand pumping chamber. It is appreciated that the alternative arrangementmay be utilized for boot injection, while the preferred arrangement maybe utilized for boot injection and square injection. Further, it isappreciated that embodiments of the present invention are not limited toany particular injection control strategies, however, embodiments of thepresent invention are particularly useful for reduced rate pilotinjection, rate shaping including boot injection, square injection, andpost injection, in addition to reducing plunger noise after injection.

[0037] Another embodiment of the present invention is illustrated inFIG. 2. An engine driven cam 32 drives plunger 34 to pressurize fuel ina pumping chamber. The valve and restriction arrangement 36 utilizes ahigh pressure restriction as part of the valve. This is different thanFIG. 1, in which the high pressure restriction may be separate from thevalve. The control valve is indicated at 38, with the injector indicatedat 40. Pumping system 30 of FIG. 2 may alternatively utilize controlvalve 44 in a similar fashion as the embodiment of FIG. 1. Further, lowpressure fuel reservoir 42 receives fuel that bypasses injector 40through control valve 38 when control valve 38 is open.

[0038] In FIG. 3, a unit pump in an exemplary implementation of theinvention is generally indicated at 50. Pump 50 includes a pump body 52defining high pressure pumping chamber 54. A plunger 56 is disposed inthe pumping chamber for pressurizing fuel. A high pressure outlet 58connects to an injector 110 through a high pressure line, optionallyincluding a check valve. A high pressure outlet is connected to thepumping chamber by the high pressure fluid line. In the unit pumpembodiment, the high pressure fluid line includes passage 60 and passage62. Passage 64 is a high pressure restriction, while passage 66 is abypass for the restriction. Control valve 70 selectively routespressurized fuel from the pumping chamber 54 to the outlet 58 or whenopen, provides pressure relief to the pumping chamber through reliefpassage 88. Valve and restriction arrangement 72 selectively directsfuel through restriction 64 or, when open, allows fuel to effectivelybypass high pressure restriction 64 through passage 66. Fuel annulus 80allows fuel to be drawn into the pumping chamber 54 through passage 88when both valves are open. O-rings 82 and 84 seal off inlet 80. Passage86 allows any leakage past plunger 56 to return to the low pressure fuelsource (not shown) connected to inlet 80.

[0039] Plunger 56 has a tail end 92 received in plunger seat 90. Aplunger spring 96 biases the plunger to the retracted position. Theplunger may be driven to the extended position by an engine driven cam(not shown). A cam follower assembly 94 receives the plunger seat andhas a cam roller 98 that is driven by a cam to urge the plunger to theextended position, compressing fuel in the pumping chamber. As theplunger is continuously driven from the retracted to the extendedposition, the valves 70 and 72 are controlled to selectively supply fuelat various pressures to outlet 58, and to injector 110. The extendedposition of the plunger is shown in phantom at 100.

[0040] With continuing reference to FIG. 3, control valve 70 includes avalve body 112 secured to an armature 114. Solenoid 116 is energized toclose the valve by pulling armature 114 towards solenoid 116. As shown,the valve is open. When closed, seating surface 120 is urged intoclosing contact with valve seat 122. A spring 118 biases the controlvalve toward the open position. Valve 72 operates in a similar fashion,and includes valve body 140 secured to armature 142. A solenoid 144 isenergized to pull armature 142 towards solenoid 144 and close the valve.The valve 72 is shown in the open position. When closed, valve seatingsurface 148 is pulled into closing contact with seating surface 150.Spring 146 biases control valve 72 toward the open position. When valve72 is closed, pressurized fuel from pumping chamber 54 is significantlyrestricted by restriction 64 to create a pressure differential betweenpumping chamber 54 and outlet 62. When valve 72 is opened, flow frompumping chamber 54 is generally unrestricted, and fuel may flow throughpassage 66. Similarly, when valve 70 is closed, pressurized fuel may berouted from chamber 54 to outlet 62, with the pressure at outlet 62possibly being reduced while valve 72 is closed. When valve 70 is open,the fuel flow from the pumping chamber may pass valve seating surface120 and return through passage 88 to the low pressure inlet 80.

[0041] It is appreciated that embodiments shown in FIG. 3 operatessimilar to the schematic shown in FIG. 1, but may alternatively bearranged to operate more similar to the schematic of FIG. 2.Alternatively, valve 72 of the valve and restriction arrangement may bereplaced with a normally closed solenoid poppet type valve or othersuitable valve as appreciated by one of ordinary skill in the art. Someflexibility is comprised by utilizing a poppet valve, but such asolution may provide a cost-effective solution for rate shape and higherinitial injection rate implementations. Specifically, the poppet valvewould not be able to reclose for post injection.

[0042] In FIG. 4, a unit injector exemplary implementation is generallyindicated at 170. Unit injector 170 includes an injector body 172 thatdefines a pumping chamber 174. A plunger 176 is driven by a cam thatdrives against plunger holder and spring seat 178. Spring 180 biases theplunger to the retracted position.

[0043] An inlet 182 supplies low pressure fuel to the unit injector.O-rings 184 and 186 effectively seal fuel inlet when the unit injectoris received in the engine block. Passage 188 connects inlet 182 to thecontrol valve and valve and restriction arrangement. The valve andrestriction arrangement is generally indicated at 196 while the controlvalve is generally indicated at 194. The valves operate similar to thevalves in the unit pump shown in FIG. 3. The output of the pumpingsystem is passage 192, which passes pressurized fuel to the injectornozzle assembly 200. Lower or needle chamber 202 receives pressurizedfuel at a pressure controlled by controlling valves 194 and 196 asplunger 176 is reciprocated. Sufficient pressure in chamber 202 causesneedle seating surface 210 of needle 204 to lift off of needle seat 212,allowing fuel to flow through passage 214 and out the end of theinjector through holes 216.

[0044] As mentioned previously, there are many implementations for thecontrol valve and the valve and restriction arrangement and theimplementation illustrated in FIGS. 3 and 4 is provided to helpfacilitate an understanding of the present invention. Specifically,FIGS. 5-8 illustrate the various relative positions of the two valvesduring various operations of the pump system in the unit pump or theunit injector. Further, the preferred arrangement for the valves isshown in FIG. 20, where a spool valve forms the valve and restrictionarrangement.

[0045] In FIG. 5, an exemplary implementation of the high pressurerestriction concept for pump systems is generally indicated at 220.Passage 222 receives pressurized fuel from the pumping chamber, whilepassage 224 directs fuel to the pump system outlet, which may be theoutlet of a unit pump or the needle chamber of a unit injector. Thecontrol valve is generally indicated at 226, while the valve andrestriction arrangement is generally indicated at 228. First valve body230 is secured to armature 232, and may be closed by actuating solenoid234. Spring 236 abuts spring seat 238 and urges valve body 230 to theopen position, as shown. Valve and restriction arrangement 228 includessecond valve body 260, which is shown in the open position. A highpressure restriction 252 allows a pressure differential to developbetween the two valves. Path 250 allows fuel to bypass the restrictionwhen valve body 260 is in the open position, as shown.

[0046] In FIGS. 6-8, like reference numerals are used to indicate likeparts from FIG. 5. Specifically, FIG. 6 illustrates the control valve inthe closed position at 270, and the valve for controlling therestriction in the closed position at 272. That is, in FIG. 6, pressurebuilds at the outlet, pressure builds at the pumping chamber, andrestriction 252 allows the pressure differential to develop between thetwo valves.

[0047] In FIG. 7, the control valve is closed at 274, while valve 276 isopen to allow fuel flow from pumping chamber to bypass the restriction.In FIG. 8, the control valve is open at 278, while the valve 280 isclosed, allowing pressure to build in the pumping chamber whilerelieving pressure at the outlet.

[0048] In FIG. 20, a preferred valve arrangement is illustrated. Becausemany components shown in FIG. 20 are similar to the components shown inFIGS. 5-8, like reference numerals have been used. Specifically, thevalve and restriction arrangement of FIG. 20 is a true spool type valve500, shown with the solenoid energized, pulling spool valve 500 to theright side of FIG. 20 and restricting fuel flow with restriction passage502. When the solenoid is de-energized, spool valve body 500 moves tothe left so that fuel flow past spool valve 500 is unrestricted. It isappreciated that the restriction may be a small diameter passage, asillustrated, or in the alternative, the restriction may be determined bythe class of fit and/or the overlap of spool valve 500 and thesurrounding pump body. That is, the restriction could be affected atarea 504.

[0049] The remaining figures, with the exception of FIG. 20, illustratethe operation of the high pressure restriction concept in a pump systemof the present invention for various injection control strategies. FIGS.9-13 illustrate utilizing the high pressure restriction concept of thepresent invention for performing a boot injection. It is appreciatedthat parameters such as cam velocity, plunger diameter, and plungercavity volume may be optimized for boot injection, square injection,post injection, or any other type of injection desired to be performedin accordance with the high pressure restriction concept, and that thevarious values for the parameters may present trade offs between thedifferent types of injections. In the following description, the termcontrol valve means the valve that controls the bypass to the lowpressure reservoir (valve 20 in FIG. 1, valve 38 in FIG. 2). Further,the term restriction valve means the valve that controls fuel flowthrough the high pressure restriction (valve 18 in FIG. 1, valve 36 inFIG. 2). Even further, the remaining figures illustrate variousinjection control strategies when the control valve is located betweenthe restriction valve and the outlet. In the alternative, somestrategies (such as boot injection or other reduced rate injections) maybe performed with the control valve between the restriction valve andthe pumping chamber. Even further, valve area means the cross-sectionalarea allowed for fluid flow through a valve.

[0050] In FIG. 9, valve area versus cam degrees is indicated at 300.Plot 302 indicates effective valve area for the restriction valve, whileplot 304 indicates effective valve area for the control valve. Plot 306indicates cam velocity. It is appreciated that FIG. 9 and the remainingfigures illustrate operation of the embodiment shown in FIG. 1 (when therestriction valve area is shown as effectively 0, fuel flows through therestriction 16 preferably having an area that is optimized for theparticular injection strategies being implemented). In FIG. 9, therestriction valve is closed to throttle fuel flow through therestriction, causing energy to be stored in the plunger cavity. Then,the control valve is closed for boot injection to begin. Opening therestriction valve releases the stored energy causing high pressureinjection.

[0051] In FIG. 10, pressure versus cam degrees is generally indicated at310 for a boot injection performed at 900 rpm (engine speed). Pumpingchamber pressure is indicated at plot 314, while pressure at the needleis indicated at 316. For reference purposes, pumping chamber plot 312indicates pumping chamber pressure in a standard pump (without the highpressure restriction). As shown, pumping chamber pressure 314 steadilyincreases, and nozzle needle pressure dramatically increases just afterthe restriction valve is opened.

[0052] In FIG. 11, fuel delivery is generally indicated at 320, andcorresponds to the pressure plots of FIG. 10. Injection rate isindicated at plot 326, while injection quantity is indicated at plot328. For reference purposes, injection rate 322 and injection quantity324 for a base implementation (without the restriction) are also shown.

[0053] In FIG. 12, pump pressure versus cam degrees is generallyindicated at 340 for a boot injection at 600 rpm (engine speed). Plot344 is the pumping chamber pressure, while plot 346 is the needlechamber pressure. For reference purposes, plot 342 illustrates pumpingchamber pressure without the high pressure restriction.

[0054] In FIG. 13, fuel delivery versus cam degrees is generallyindicated at 350, and corresponds to the pressure plots of FIG. 12.Injection rate is indicated at plot 356 while injection quantity isindicated at plot 358. For reference purposes, base injection rate plot352 and base injection quantity plot 354 (no high pressure restriction)are also provided.

[0055] FIGS. 14-16 illustrate performance of a square injection. In FIG.14, valve area versus cam degrees is generally indicated at 370. Thecontrol valve is indicated at 374 while the restriction valve isindicated at 372. Plunger velocity is indicated at 376. As shown, therestriction valve is closed to store pressure in the pumping chamber.The control valve is closed and the restriction valve is opened atnearly the same time to cause a high initial rate of injection at justpast 390 degrees.

[0056] In FIG. 15, pump pressure versus cam degrees for square injectionat approximately 900 rpm (engine speed) is indicated at 380. Pumpingchamber pressure is indicated at 386, while needle chamber pressure isindicated at 388. Base (without the high pressure restriction) pumpingchamber pressure plot 382 and needle chamber pressure plot 384 areprovided for reference purposes.

[0057] In FIG. 16, square injection at 900 rpm is illustrated at 400.

[0058] Injection rate plot 406 and injection quantity plot 408illustrate the utilization of a high pressure restriction concept forperforming the square injection. For reference purposes, base injectionrate plot 402 and base injection quantity plot 404 are provided (norestriction).

[0059] In FIG. 17, valve are versus cam degrees for a post injection isgenerally indicated at 420. Valve area for the restriction valve isindicated at plot 422, while valve area for the control valve isindicated at plot 424. As shown, at about 390 degrees, the control valveis closed and the restriction valve is open for a main injection, whileat about 400 degrees, the restriction valve is closed and the controlvalve is open to end the main injection. Then, the control valve isre-closed for a post injection, and the restriction valve is open torelease the pressure stored in the pumping chamber. Thereafter, thecontrol valve is then opened to end the post injection.

[0060] In FIG. 18, pressure versus degrees for a post injection at about900 rpm (engine speed) is indicated at 440. Pumping chamber pressure isindicated at plot 446, while needle chamber pressure is indicated atplot 448. As shown by plot 448, a main injection is followed by a postinjection. Baseline pumping chamber pressure plot 442 and needle chamberpressure plot 444 are provided for reference purposes (no restriction).

[0061] In FIG. 19, fuel delivery for post injection at 900 rpm isgenerally indicated at 460. Plot 466 illustrates injection rate, whileplot 468 illustrates injection quantity. Portion 470 of plot 466illustrates injection rate for the post injection. Base injection rateplot 462 and injection quantity plot 464 (without the high pressurerestriction concept) are provided for reference purposes).

[0062] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andit is understood that various changes may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A pump system for a fuel injection system, thepump system comprising: a body defining a high pressure pumping chamber;a plunger disposed in the pumping chamber for pressurizing fuel; a highpressure outlet; a high pressure fluid line connecting the pumpingchamber to the outlet; a control valve along the fluid line, the controlvalve including a first valve body movable between a closed position inwhich pressurized fuel is routed from the pumping chamber to the outletand an open position in which pressure relief is provided to the fluidline; and a valve and restriction arrangement along the fluid line,including a restriction and a second valve body, the second valve bodybeing movable between an open position in which fuel flow from thepumping chamber is generally unrestricted by the restriction and aclosed position in which fuel flow from the pumping chamber issignificantly restricted by the restriction to store energy in thepumping chamber.
 2. The system of claim 1 wherein the body is a unitpump body, and the high pressure outlet is configured for flowcommunication with a fuel injector.
 3. The system of claim 1 wherein thebody is a unit injector body and defines a needle chamber, the pumpfurther comprising: an injector nozzle assembly in flow communicationwith the high pressure outlet, the assembly including a needle receivedin the needle chamber, the needle chamber receiving pressurized fuelfrom the pump outlet.
 4. The system of claim 1 wherein the second valvebody configured as a pressure-balanced valve.
 5. The system of claim 4wherein the second valve body open position provides a flowcross-sectional area, not including any effective flow cross-sectionalarea of the restriction, of about two to three millimeters squared. 6.The system of claim 1 wherein the second valve body is configured as apressure-balanced valve utilizing a through passage as the restriction.7. The system of claim 1 wherein the valve and restriction arrangementis located between the pumping chamber and the control valve.
 8. Thesystem of claim 1 wherein the valve and restriction arrangement islocated between the control valve and the outlet.
 9. A method ofcontrolling a pump system for a fuel injection system, the pump systemhaving a body defining a high pressure pumping chamber, a plungerdisposed in the pumping chamber for pressurizing fuel, a high pressureoutlet, a high pressure fluid line connecting the pumping chamber to theoutlet, and a control valve along the fluid line, the control valveincluding a first valve body movable between a closed position in whichpressurized fuel is routed from the pumping chamber to the outlet and anopen position in which pressure relief is provided to the fluid line,the method comprising: controlling a valve and restriction arrangementalong the fluid line, including a restriction and a second valve body,the second valve body being movable between an open position in whichfuel flow from the pumping chamber is generally unrestricted by therestriction and a closed position in which fuel flow from the pumpingchamber is significantly restricted by the restriction to store energyin the pumping chamber, the valve and restriction arrangement beingcontrolled so as to control fuel flow from the pumping chamber to theoutlet.
 10. The method of claim 9 further comprising: closing thecontrol valve for an injection by moving the first valve body to theclosed position; and restricting fuel flow from the pumping chamber bymoving the second valve body to the closed position to reduce aninjection rate, while the control valve is closed.
 11. The method ofclaim 9 further comprising: closing the control valve for an injectionby moving the first valve body to the closed position; restricting fuelflow from the pumping chamber by moving the second valve body to theclosed position to reduce an injection rate, while the control valve isclosed; and thereafter, opening the control valve by moving the firstvalve body to the open position.
 12. The method of claim 9 furthercomprising: closing the control valve for an injection by moving thefirst valve body to the closed position; restricting fuel flow from thepumping chamber by moving the second valve body to the closed positionto reduce an injection rate and store energy in the pumping chamber,while the control valve is closed; unrestricting fuel flow from thepumping chamber by moving the second valve body to the open position toincrease the injection rate, while the control valve is closed; andthereafter, opening the control valve by moving the first valve body tothe open position.
 13. The method of claim 9 wherein the valverestriction arrangement is located between the pumping chamber and thecontrol valve and wherein the method further comprises: opening thecontrol valve by moving the first valve body to the open position;restricting fuel flow from the pumping chamber by moving the secondvalve body to the closed position to store energy in the pumpingchamber, while the control valve is open; thereafter, closing thecontrol valve by moving the first valve body to the closed position; andunrestricting fuel flow from the pumping chamber by moving the secondvalve body to the open position to increase the injection rate, whilethe control valve is closed.
 14. The method of claim 9 wherein the valverestriction arrangement is located between the pumping chamber and thecontrol valve and wherein the method further comprises: closing thecontrol valve by moving the first valve body to the closed position;unrestricting fuel flow from the pumping chamber by moving the secondvalve body to the open position, while the control valve is closed; andthereafter, opening the control valve by moving the first valve body tothe open position; and restricting fuel flow from the pumping chamber bymoving the second valve body to the closed position to reduce pressurerelease at the plunger, while the control valve is open.
 15. The methodof claim 14 further comprising: thereafter, closing the control valve bymoving the first valve body to the closed position.
 16. The method ofclaim 15 further comprising: thereafter, unrestricting fuel flow fromthe pumping chamber by moving the second valve body to the open positionto increase an injection rate, while the control valve is closed.